1. Technical Field
The present disclosure relates to a fiber measurement device for measuring characteristics of an optical fiber.
2. Related Art
An OTDR (Optical Time Domain Reflectometer) is known as a device for measuring characteristics of an optical fiber (hereinafter referred to as a fiber). The OTDR inputs a light pulse (laser light) from a laser light source to a fiber and then detects backscattered light (Rayleigh scattered light) and Fresnel reflected light from the fiber. Thereby, the OTDR measures and displays a loss distribution state of the fiber.
FIG. 9 shows a fiber measurement device 101 as an example of a conventional OTDR. In FIG. 9, the fiber measurement device 101 measures a loss distribution state of a fiber 102. The fiber measurement device 101 has a driver circuit 103, a laser diode 104, an optical coupler 105, a photodetector 106, a signal amplifier circuit 107, a control processing circuit 108 and a display device 109.
The driver circuit 103 supplies driving power to the laser diode 104. The laser diode 104 uses the driving power to emit laser light. The optical coupler 105 is a means for branching the laser light. The optical coupler 105 transfers the laser light emitted from the laser diode 104 to the fiber 102. In the fiber 102, backscattered light and Fresnel reflected light are generated. The generated light is reflected by the optical coupler 105 to be input to the photodetector 106.
The photodetector 106 detects laser light to generate a current by photoelectric conversion. The generated current is converted to a voltage signal. The voltage signal is amplified by the signal amplifier circuit 107. The control processing circuit 108 performs predetermined signal processing on the amplified voltage signal. Then, the processed signal is displayed on the display device 109. Moreover, the control processing circuit 108 controls the driver circuit 103 to control the emission of the laser light.
FIG. 10 shows backscattered light level displayed on the display device 109 in a case where the fiber 102 has a fusion splice point, a connection point (connector) and a bending loss point. Here, an end of the fiber 102 is an open end. As shown in FIG. 10, the backscattered light level regarding the laser light input to the fiber 102 changes greatly at respective positions of the fusion splice point, the connection point (connector) and the bending loss point of the fiber 102. Moreover, the backscattered light level changes much further at the open end.
The graph shown in FIG. 10 shows the loss distribution state of the fiber 102. The loss distribution state is displayed on the display device 109, and thereby characteristics of the fiber 102 can be recognized. A photon counting method is known as another method for measuring characteristics of a fiber. According to the photon counting method, the number of photons that is proportional to light intensity of laser light fed back from the fiber is counted and then photon probability is used for revealing the characteristics of the fiber. A combined technique of the photon counting method and the method of the OTDR is disclosed in JP-A-2006-184038.